The background art teaches various formulations for blending an aqueous PTFE dispersion with various additives and/or adjuvants designed for specific purposes. For example, U.S. Pat. No. 4,990,544 teaches a gasket comprising a fibrillated PTFE resin and a fine inorganic powder dispersed therein. U.S. Pat. No. 4,985,296 teaches an expanded, porous PTFE film containing filler material which is purposely compressed to provide thin films where space reduction is desirable.
Assignee's patent application U.S. Ser. No. 07/639,515 (now allowed) discloses a method of controlling the porosity in a composite PTFE article by controlling the amount of lubricant used during processing of the article. The article also has controlled mean pore size. Design News, "Particulates Captured/Carried by Fibrillated PTFE", Feb. 9, 1987 (Cahners Publishing Company), discloses particles carried by fibrillated PTFE membranes having a porosity in the range of 30 to 70%, and pore sizes from 0.01 to 5.0 microns.
U.S. Pat. Nos. 4,971,736, 4,906,378, and 4,810,381 disclose a composite chromatographic sheet-like article and method therefor. The article comprises a PTFE fibril matrix and non-swellable sorptive hydrophobic particles enmeshed in the matrix. References cited in these patents relate to other PTFE matrices containing particulates. U.S. Pat. No. 4,971,697 teaches a chromatographic article comprising a PTFE fibril matrix having enmeshed therein a mixture of non-swellable sorptive particles and hydrated silica flakes. Hagen, et al., "Membrane Approach to Solid Phase Extractions", Analytica Chimica Acta, 236 (1990) 157-164, relates to particle loaded PTFE matrices useful in extraction applications.
U.S. Pat. No. 4,460,642 teaches a water-swellable composite sheet of microfibers of PTFE and hydrophilic absorptive particles enmeshed therein which is useful as a wound dressing.
U S. Pat. No. 4,923,737 discloses a method for a "metal cloth" prepared from fibrillated PTFE containing metal or other particles entrapped in the fibrils.
In regard to polymers, fibrillated PTFE has also been combined with a polyamide to provide articles by extrusion blow-molding (U.S. Pat. No. 4,966,941) and with an elastomer to provide articles with increased durability (U.S. Pat. No. 4,962,136). U.S. Pat. No. 4,945,125 teaches a process of producing a fibrillated semi-interpenetrating polymer network of PTFE and silicone elastomer. U.S. Pat. No. 4,914,156 describes a blow moldable composition comprising a polyether, an epoxide polymer, a source of catalytic cations, and a fibrillatable PTFE. U.S. Pat. No. 4,902,747 discloses a polyarylate composition containing fibrillatable PTFE.
U.S. Pat. Nos. 4,199,628 and 4,265,952 relate to a vermicular expanded graphite composite blended with a corrosion resistant resin such as PTFE with improved impermeability to corrosive fluids at high temperatures.
U.S. Pat. No. 4,483,889 discloses the method of making a composite material comprised of a fibrous matrix, expandable polymeric microbubbles, and a formaldehyde-type resin involving distributing the expandable microspheres (either expanded or unexpanded) into the fiber matrix, expanding the polymeric bubbles by application of heat (in the case where unexpanded microbubbles were used), and impregnating the resulting porous matrix with a curable formaldehyde-type resin to give a foam.
U.S. Pat. Nos. 3,407,096, 3,407,249, 3,556,161, and 3,281,511 teach incorporation of extractable or leachable filler particles to create porosity in an article.